This invention relates generally to a container for a radioactive substance and more particularly, but not by way of limitation, to a container for connecting to a flow line extending between a blending tub and a well head.
Throughout an oil or natural gas well's life, there may be the need to "tag" a particular operation with one or more liquefied or slurried radioactive tracer sources. These operations include fracturing, acidizing, cementing and others known to the art. One particular type of tracer source is a proppant, such as sand, coated or otherwise containing a radioactive isotope. Once such a source becomes entrapped or deposited in fractures or voids in the well bore, subsequent gamma ray logging operations can be used to locate where such source is entrapped or deposited, thereby providing information related to how effective the particular operation was.
The use of radioactive sources can create problems in shipping and using the sources. For example, in shipping a radioactive substance, suitable shipping containers meeting governmental regulations must be used. These shipping containers have frequently been of the type requiring manual handling by personnel at a camp site or well site in transferring the radiactive substance from each of the containers to a blending tub or other reservoir used in a method for injecting a radioactive mixture into a well. Such handling can lead to personnel, equipment and environmental exposure to, and contamination by, the radioactivity.
I am aware of three methods for adding a radioactive source to one or more other materials which are to be mixed and conveyed into a well. One of these methods includes manually adding the tracer source, such as from glass bottles, into the mixing tub of a blender unit, a cement unit or other source equipment from which the resultant mixture is ultimately to be pumped into the well. This is likely the easiest method to use; however, it also likely poses the greatest risk of an accident resulting in exposure and contamination to personnel and the environment. Because the mixing tub into which the radioactive substance is poured is at or near the head of the flow stream ultimately moved into the well through suitable conduits and pumps, this is also the method which contaminates the most equipment generally not dedicated solely to use with the radioactive substances.
A second method utilizes a low pressure injector to inject the radioactive tracer source before one or more high pressure pumps used to pump a mixture from a blending unit into a well. Such an injector unit is usually skid-mounted and transported in a utility trailer. This unit typically comprises a diaphgram pump, a reservoir funnel, a metering valve, a visual sight tube, valves, and a length of transfer hose for injecting the tracer source into the flow stream flowing between the blending unit and the high pressure pump. This type of unit may weigh about 400 pounds and cost between $7,000.00 and $10,000.00. Although this unit eliminates contamination of the upstream blending equipment and an upstream portion of the suction line of the high pressure pumps, which upstream components would be contaminated by the first-mentioned method, this second method still requires personnel to manually open the shipping containers and transfer the radioactive isotope to the reservoir funnel. Therefore, there is still a significant risk of human and environmental contamination. Furthermore, the high pressure side of the pumping equipment is still contaminated. The equipment of the injector unit and the transfer hose are also contaminated and thus need to be carefully handled even though they are dedicated to this specific use and are not intended to be used with non-radioactive substances that might thereby by contaminated by residue in the injector unit. Furthermore, the injector unit of this type of method is not designed to transport the radioactive tracer material from location to location. The tracer must be carried in separate containers and transferred to the unit at the well site.
A third method uses a high pressure liquid tracer injection trailer including a dual reservoir tracer container meeting governmental regulations so that it can be used to transport the radioactive source. A particular embodiment of this container is designed to receive a separate container which includes a radioactive material-loaded syringe carried in a protective housing directly connectible to the dual reservoir container. The injection unit of this third method also includes a metering pump, a high pressure metering-dilution pump, and a hose to transfer the tracer source to the well head. Such a trailer can weigh between 3,000 and 3,500 pounds and cost between $25,000.00 and $30,000,00. This unit is designed to inject only a liquid tracer source, not a slurry type of source. Because this unit injects the radioactive material the closest to the well head of the three mentioned methods, this method produces the least contamination of equipment located at the well site. Furthermore, this unit can legally transport the radioactive tracer source; however, loading of the tracer source is still to be conducted by personnel at a field camp (such as by means of the syringe-carrying housing) and not at a central production location where the safest procedures may most likely be observed.
Thus, although the three methods do have respective advantages and the third-mentioned method likely creates the least likelihood for personnel, environmental and equipment contamination, even it still is generally implemented by transferring radioactive substances at locations where the safest handling precautions might not or cannot be observed. Therefore, there is the need for an improved container which overcomes shortcomings of the aforementioned techniques by functioning both as a carrying cartridge in which a radioactive substance can be legally transported and as an injector from which the radioactive substance can be injected directly into the mixture flowing into the well bore in such a manner to reduce the risk of personnel, equipment and environmental exposure and contamination. Such a container should be designed so that it is to be loaded at a central loading facility to obviate any transfers by personnel at a field camp or well site or other location where proper handling procedures may be more likely ignored or impossible to follow. The container should be designed so that its contents can be unloaded directly into the flowing stream of material between a blending tub and a well head to reduce the amount of contaminated equipment and to reduce the risk of exposing or contaminating personnel or the environment. The container should be able to hold and inject a premixed slurry as well as a radioactive source in more fluid form. The container should not require its own pumping equipment or hoses to be operational, thereby reducing the size and cost of the unit. The container should be constructed to meet pertinent governmental regulations for radioactive material shipping containers so that it can be used to transport a radioactive substance from the loading site to the use site. The container should be adaptable to both high and low pressure usage and to usage at various rates of injection. The container should be relatively lightweight and inexpensive and yet be reusable to further enhance its economic aspects.